For the sibling mosquito species Aedes triseriatus Say and Ae. hendersoni Cockerell, success of offspring is highly dependent on oviposition site selection by gravid females, and the dynamics of that selection process have been the subject of much investigation. Patterns of vertical oviposition stratification were examined in this study by placing basal and canopy level oviposition traps in relatively steep and flat terrains, as well as in flood-prone riverbank vs upland settings. Strong stratification existed in both steep and flat terrains, with Ae. triseriatus favoring basal ovitraps and Ae. hendersoni favoring canopy ovitraps. Contrary to expectations, Ae. hendersoni displayed even more marked preference for canopy ovitraps in steeper terrain. Both species avoided basal ovitraps in flood-prone locations, where Ae. triseriatus oviposited only in canopy ovitraps and greatly outnumbered Ae. hendersoni in canopy ovitraps. In contrast, the expected stratification was found in nearby upland habitats.